Elevators are essential devices for moving passengers and cargo up and down within tall buildings. In order to operate elevators safely, a number of safety devices have been employed and improved over the years. One of those systems is referred to as a governor. Governors are constructed such that if the elevator car surpasses a predetermined safe speed, the governor will engage to slow down and ultimately stop the car from further movement. This can be accomplished by engaging a wedge or other type of a mechanical brake as will be further described herein.
One known type of governor is referred to as a pendulum-type governor. With a pendulum type governor, a sheave is mounted on a horizontal shaft provided at the top of a hoistway in which the machine elevator is operated. A cable, rope, belt or the like is operatively connected from the sheave to the elevator car itself. In addition to the sheave, the shaft is connected to a gearbox, which in turn is connected to a vertically oriented shaft. First and second pendulums are connected by linkages to the vertical shaft. If the elevator car increases in speed, the rotational speed of both shafts increases as well. The pendulums are spring biased into a non-extended position, but when the elevator car surpasses a predetermined speed, the biasing force of the spring will be overcome and the pendulums will swing outwardly, thereby causing the governor to engage. This may be accomplished by first locking the sheave and rope against further motion. Once the rope stops and the elevator car continues to move, the rope pulls up on a safety gear, thereby causing a wedge-type friction roller, solid plate, or the like to clamp very tightly on running guides of the elevator car. While effective, pendulum-type governors do have a significant space requirement given the need for the vertical shaft and gearbox.
Another type of governor is known as a flyweight-type governor. With a flyweight-type governor, a plurality of flyweights are eccentrically mounted about the shaft of the sheave, and connected by spring-biased linkages. As the sheave and flyweights rotate, centrifugal force tends to cause the flyweights to pivot radially outwardly. The spring is sized such that its biasing force is overcome when the sheave rotates beyond a predetermined safe speed and thus the generated centrifugal force is greater than the spring biasing force. When this happens the governor engages to slow and ultimately stop the elevator car in a manner similar to a pendulum-type governor. While more compact than pendulum-type governors, flyweight-type governors are more prone to false trips, and thus unnecessary stoppages of the elevator. More specifically, due to the center of gravity of the flyweights not being aligned with the center of gravity with the sheave, flyweight-type governors are very sensitive to false trips caused by high acceleration or deceleration of the car even when the overall speed of the car has not exceeded the predetermined safe velocity.
It can therefore be seen that a need exists for an elevator governor with lessened space requirements compared to pendulum-type governors, and with a decreased propensity toward false trips compared to flyweight-type governors.